The present invention relates to shearing and coiling metal strip. In particular, it is concerned with guiding the strip onto a coil at the end of a rolling mill line, and shearing the strip and transferring the strip to a second coil when a first coil is complete, whilst at the same time permitting the continuous production of the strip at an uninterrupted rate.
Such shear and guiding systems for shearing and guiding the strip to alternate coils are well known in the art. In fact, more than two coils may be used if the cycle time for the removal of the completed coil is greater than the time to complete the coiling of a single coil.
In a typical known system, the strip is first passed through a rotating shear unit, which comprises two cutting edges each mounted on a rotatable support on opposite sides of the strip so that the blades are coincident with the strip and act together to cut the strip when the rotatable supports are rotated. The rotatable supports rotate in the direction of the strip. The strip emerges from the shears towards two pairs of deflecting rolls placed one after the other. Each pair of deflecting rolls has an associated spool or mandrel located below the straight path from the shears. Various deflector plates are used in combination with the deflector rolls to guide the strip onto the spool or mandrel.
Supposing that the strip is being wound on the second spool, the first deflecting rolls will be open, allowing the strip to pass through them without deflection and on towards the second pair of deflecting rolls, which will deflect the strip to its associated spool. As that spool becomes nearly full, the strip is sheared and the part ahead of the shears will continue along the existing strip path, and will be wound onto the current spool.
As the end of that part passes through the first deflecting rolls and the front edge of the next part of the strip approaches those deflecting rolls, those rolls will be operated to engage with the strip and deflect it onto the spool associated with those rolls. That spool is then filled to form the next coil whilst the previous coil is removed from its spool.
When the second spool is nearly full, the shears are again operated, and the deflecting rolls associated with that spool are opened to allow the front edge of the new part of the strip to pass straight through and on to the deflecting rolls associated with the second spool, which should by then have been changed in readiness.
This known system is typical of the way that strip is formed into coils at the end of the strip production. There are variations on this theme in which the spools are movable to pick up the strip after each cut, and also there are alternative means of diverting the path of the strip, some of which rely merely on gravity or the inertial movement of the strip to cause the strip to take up a new path.
These known systems have the disadvantage that it is necessary to control the time of engagement of the guiding rolls or guiding mechanism accurately, immediately after the cutting has taken place. This can cause problems for the cutting and coiling of thin strip moving at high strip speeds. If the guiding rolls are engaged too soon, then the previous strip length will be engaged and this will cause it to be deflected in the wrong direction. Alternatively if the engaging roll is engaged too late, the next strip length will proceed on its previous path and may overshoot the corresponding spool. Thus the engaging roll must move very quickly into and out of position, and the dynamic limitations of this movement of the engaging rolls limits the strip speeds that can be used. Thus it is necessary to ensure that the movement of the guiding rolls is precisely timed with the action of the rotating shears.
A further disadvantage of known systems is that thin strip especially is very easily bent by hitting stationary guides or other guidance mechanisms which can throw the strip out of line with the desired path into the coiling stage or cause it to jam. Similarly, for systems which rely on inertia or gravity, the strip speeds are limited because at high speeds the strip may not fall in time or in a predictable way because it is influenced by aerodynamic effects.
For cold rolling, a technique known as carousel coiling has been developed. For this technique, there is provided apparatus for coiling successive lengths of metal strip onto mandrels, comprising means for changing the strip path from a path leading to the mandrel currently being wound to a path to a new mandrel when the current strip ends and a new strip appears, wherein the new mandrel is positioned in an initial position such that the strip path to it is a straight path, and means are provided for moving that mandrel to a second position such that the strip path to it is an angled path the first segment of which is common with the first part of the straight strip path.
The tail end of the old length of strip is pulled along the angled path by the main body of that length which is already coiled on its mandrel, and therefore cannot go seriously astray. After the shear is operated, the leading edge of the new length of strip continues straight ahead instead of following the angled path because of the inertia and weight of the strip. The leading edge of the new length of strip is guided onto the mandrel by a moving belt which is wrapped part of the way around the mandrel in such a way that the leading edge of the new length of strip is caught between the belt and the mandrel. This type of apparatus is known as a belt wrapper.
The present invention is particularly concerned with handling hot thin strip. This involves a number of additional problems compared to handling strip resulting from cold rolling.
Mills rolling cold strip generally slow down during the changeover from one coiling mandrel to the other. This reduces the aerodynamic effects on the strip which could cause it to take the wrong path. It also reduces the speed at which the belt wrapper or other strip guidance mechanism has to operate. However, hot strip mills cannot slow down during coiling for metallurgical reasons. Consequently, the belt wrapper or other guidance mechanism has to operate at full speed. The life of conventional belt materials or chains is severely reduced by operating at the high speeds required for thin hot strip. In addition the high temperature of the strip is liable to cause damage to the belt or chain material.
In addition, guidance of the strip is more difficult because the hot strip has lower strength than cold strip and is therefore more liable to bend and follow an incorrect path; also, with higher speeds, aerodynamic effects are more liable to cause deflection of the head of the strip from the desired path.
The general object of the invention is to provide means for improved guidance of hot rolled strip in strip shearing and coiling apparatus.